// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.IO;
using System.Linq;
using System.Reflection;
#if NETCOREAPP2_1
using System.Runtime.Loader;
#endif
using Microsoft.Extensions.CommandLineUtils;
using Microsoft.Extensions.Tools.Internal;

namespace Microsoft.Extensions.ApiDescription.Tool.Commands
{
    internal class GetDocumentCommand : ProjectCommandBase
    {
        private CommandOption _fileListPath;
        private CommandOption _output;

        public GetDocumentCommand(IConsole console) : base(console)
        {
        }

        public override void Configure(CommandLineApplication command)
        {
            base.Configure(command);

            _fileListPath = command.Option("--file-list <Path>", Resources.FileListDescription);
            _output = command.Option("--output <Directory>", Resources.OutputDescription);
        }

        protected override void Validate()
        {
            base.Validate();

            if (!_fileListPath.HasValue())
            {
                throw new CommandException(Resources.FormatMissingOption(_fileListPath.LongName));
            }

            if (!_output.HasValue())
            {
                throw new CommandException(Resources.FormatMissingOption(_output.LongName));
            }
        }

        protected override int Execute()
        {
            var thisAssembly = typeof(GetDocumentCommand).Assembly;

            var toolsDirectory = ToolsDirectory.Value();
            var packagedAssemblies = Directory
                .EnumerateFiles(toolsDirectory, "*.dll")
                .Except(new[] { Path.GetFullPath(thisAssembly.Location) })
                .ToDictionary(path => Path.GetFileNameWithoutExtension(path), path => new AssemblyInfo(path));

            // Explicitly load all assemblies we need first to preserve target project as much as possible. This
            // executable is always run in the target project's context (either through location or .deps.json file).
            foreach (var keyValuePair in packagedAssemblies)
            {
                try
                {
                    keyValuePair.Value.Assembly = Assembly.Load(new AssemblyName(keyValuePair.Key));
                }
                catch
                {
                    // Ignore all failures because missing assemblies should be loadable from tools directory.
                }
            }

#if NETCOREAPP2_1
            AssemblyLoadContext.Default.Resolving += (loadContext, assemblyName) =>
            {
                var name = assemblyName.Name;
                if (!packagedAssemblies.TryGetValue(name, out var info))
                {
                    return null;
                }

                var assemblyPath = info.Path;
                if (!File.Exists(assemblyPath))
                {
                    throw new InvalidOperationException(
                        $"Referenced assembly '{name}' was not found in '{toolsDirectory}'.");
                }

                return loadContext.LoadFromAssemblyPath(assemblyPath);
            };

#elif NET461
            AppDomain.CurrentDomain.AssemblyResolve += (source, eventArgs) =>
            {
                var assemblyName = new AssemblyName(eventArgs.Name);
                var name = assemblyName.Name;
                if (!packagedAssemblies.TryGetValue(name, out var info))
                {
                    return null;
                }

                var assembly = info.Assembly;
                if (assembly != null)
                {
                    // Loaded already
                    return assembly;
                }

                var assemblyPath = info.Path;
                if (!File.Exists(assemblyPath))
                {
                    throw new InvalidOperationException(
                        $"Referenced assembly '{name}' was not found in '{toolsDirectory}'.");
                }

                return Assembly.LoadFile(assemblyPath);
            };
#else
#error Target frameworks need to be updated.
#endif

            // Now safe to reference the application's code.
            try
            {
                var assemblyPath = AssemblyPath.Value();
                var context = new GetDocumentCommandContext
                {
                    AssemblyPath = assemblyPath,
                    AssemblyName = Path.GetFileNameWithoutExtension(assemblyPath),
                    FileListPath = _fileListPath.Value(),
                    OutputDirectory = _output.Value(),
                    ProjectName = ProjectName.Value(),
                    Reporter = Reporter,
                };

                return new GetDocumentCommandWorker(context).Process();
            }
            catch (Exception ex)
            {
                Reporter.WriteError(ex.ToString());
                return 2;
            }
        }

        private class AssemblyInfo
        {
            public AssemblyInfo(string path)
            {
                Path = path;
            }

            public string Path { get; }

            public Assembly Assembly { get; set; }
        }
    }
}
